1. Technical Field
The present invention relates to an image forming apparatus and an image forming method which perform image formation by developing an electrostatic latent image formed on an image carrier by liquid developer having toner and carrier liquid, and transferring and fixing a developed developer image to a recording material.
2. Related Art
Various image forming apparatuses have been proposed in which electrostatic latent images are developed and visualized using high-viscosity liquid developer where toner composed of solid components is dispersed in a liquid solvent used as a carrier liquid. The developer used in the image forming apparatuses is an agent where solid components (toner particles) are suspended in an electrically isolating high-viscosity organic solvent (carrier liquid) composed of silicon oil, mineral oil, cooking oil or the like. Extremely fine particles of which the particle diameter is 1 μm or so are used as the toner particles, a high quality can be achieved compared to dry image forming apparatuses in which a particle diameter of 7 μm is used as in related art.
As the image forming apparatus using such liquid developer, for example, an image forming apparatus in which a developing roller is in contact with a photoreceptor to thereby perform development is disclosed in JP-A-2008-170602, U.S. Pat. No. 5,610,694, and U.S. Pat. No. 5,737,666. In particular, as disclosed in the forty-sixth paragraph of JP-A-2008-170602, when the compressed state of toner is weak, it has known that a vertically streaky image disorder called a rivulet in a developing nip is generated. This phenomenon is attributed to the fact that the movement velocity of the toner particles at the developing nip is not sufficient due to the weak compression of the toner, and thus the press to the photoreceptor is not sufficient, and as a result, the liquid developer causes a cobweb phenomenon in a developing nip outlet formed between the developer carrier and the photoreceptor.
Such a rivulet generated on the photoreceptor (which is called a “developer stripe” in the present specification) affects even an image transferred to a recording material such as paper, to thereby exhibit image unevenness in the transferred image.
On the other hand, one cause which generates image unevenness is attributed to the feed roller (anilox roller). The feed roller is a roller in which a diagonal-shaped groove is formed on the surface finely and uniformly, and feeds the liquid developer drawn up through this groove to the developing roller. A developer pattern generated by the groove typically vanishes when fed to the developing roller, and a thin film of the uniform developer is formed on the developing roller. However, there may be a case where the developer pattern does not vanish even on the developing roller and is transferred due to various types of environmental changes, such as variation in a viscosity of the liquid developer due to the change of temperature, whereby the developer pattern appears as image unevenness on the photoreceptor.